CVE-2026-55898: Microsoft Office Excel out-of-bounds read

CVE-2026-55898 · Severity: medium · CVSS 6.1 · Published 2026-07-14

Microsoft Excel, a widely used spreadsheet application, contains a security vulnerability that could allow an attacker to access sensitive information. To exploit this, an attacker would typically need to trick a user into opening a specially crafted Excel file. Successful exploitation could lead to the unauthorized disclosure of data or cause the application to crash, potentially disrupting business operations.

Technologies: Microsoft 365 Apps for Enterprise, Microsoft Excel 2016, Microsoft Office 2019, Microsoft Office 365 for Mac, Microsoft Office LTSC 2021, Microsoft Office LTSC 2024, Microsoft Office LTSC for Mac 2021, Microsoft Office LTSC for Mac 2024, Microsoft Office Online Server. Vendors: Microsoft.

Quick answers

Is CVE-2026-55898 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-55898 being exploited in the wild.
How severe is CVE-2026-55898?
Medium severity, with a CVSS score of 6.1, published 14 July 2026.
Which products and versions are affected?
Microsoft 365 Apps for Enterprise versions prior to July 2026 updates; Microsoft Excel 2016 versions prior to 16.0.5561.1001; Microsoft Office 2019 versions prior to July 2026 updates; Microsoft Office 365 for Mac versions prior to 16.111.26071215; and 5 more.
Is there a fix for CVE-2026-55898?
No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.
How is CVE-2026-55898 attacked?
It is attacked with local access, in a network appliance.
Am I affected by CVE-2026-55898?
Check whether you run Microsoft 365 Apps for Enterprise, Microsoft Excel 2016, Microsoft Office 2019 or one of the others listed at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Technical details

An out-of-bounds read vulnerability (CWE-125) exists in multiple versions of Microsoft Excel and Office products. The flaw is triggered when the application fails to properly validate input while reading from a memory buffer, which can be exploited by an attacker who convinces a user to open a malicious file. While the primary impact is local information disclosure, the CVSS vector also indicates a high impact on availability, suggesting the flaw may cause application instability or crashes. Microsoft has released security updates to address this issue across affected platforms including Windows and macOS.

Affected products

  • Microsoft Microsoft 365 Apps for Enterprise versions prior to July 2026 updates
  • Microsoft Microsoft Excel 2016 versions prior to 16.0.5561.1001
  • Microsoft Microsoft Office 2019 versions prior to July 2026 updates
  • Microsoft Microsoft Office 365 for Mac versions prior to 16.111.26071215
  • Microsoft Microsoft Office LTSC 2021 versions prior to July 2026 updates
  • Microsoft Microsoft Office LTSC 2024 versions prior to July 2026 updates
  • Microsoft Microsoft Office LTSC for Mac 2021 versions prior to 16.111.26071215
  • Microsoft Microsoft Office LTSC for Mac 2024 versions prior to 16.111.26071215
  • Microsoft Office Online Server versions prior to 16.0.10417.20175

Timeline

  • 2026-07-14: disclosed
  • 2026-07-14: advisory

References

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